In polymer composite manufacturing the use of high loadings of mineral fillers increases the weight of the part beyond the optimum. If the same part could be made with fewer raw materials the part would be both lighter and more cost effective. Many techniques have been used to lower heavily mineral-filled composites weight. One of the most common methods is to use microspheres to replace some of the mineral filler. In a thermoset resin system such as unsaturated polyester there are some limitations to micro sphere filler systems.
Light weight microspheres tend to float on the liquid unsaturated polyester and are difficult to wet out by the resin. In addition, dry light weight filler systems become dusty and difficult to handle as they get lower and lower specific gravities. Moreover, microspheres are usually more expensive than the mineral fillers that they replace.